Various actuators have conventionally been proposed in which a movable body is oscillated by means of an electrostatic force generated by an electrostatic comb element. These actuators are manufactured by using a silicon substrate or the like with a micro electro mechanical system (MEMS) technique to which a semiconductor process is applied. A rotary actuator can be taken as an actuator used for optical scanning or the like.
As the rotary actuator described above, a technique has been proposed in which an oscillator device having regions electrically separated vertically in the thickness direction is formed by utilizing a silicon on insulator (SOI) substrate. Specifically, there has been proposed the one having the structure in which an electrostatic movable comb element mounted to a movable body and an electrostatic stationary comb element mounted to a support portion are electrically separated vertically in the thickness direction of the substrate (see Japanese Patent Application Laid-Open No. 2006-154315).
The rotary actuator disclosed in Japanese Patent Application Laid-Open No. 2006-154315 is manufactured by using an SOI substrate obtained by laminating plural silicon layers through an insulating film. Therefore, the oscillating movable body can be electrically separated vertically by the insulating layer in the thickness direction of the substrate. With this structure, an upward force and a downward force are respectively applied in the thickness direction of the substrate by exerting the electrostatic force on both ends of the movable body, so that the movable body can be rotated about a certain shaft. As described above, a rotation toward the outside of the plane of the substrate can be produced by using this structure in the movable body formed by the substrate.
The actuator having the structure disclosed in Japanese Patent Application Laid-Open No. 2006-154315 produces force in the rotating direction by the electrostatic force. On the other hand, some electrostatic forces are also produced in the direction of suppressing the rotation at that time. This is because the movable body includes electrically separated plural regions, on which the electrostatic forces are exerted in different directions with respect to the rotating direction depending upon the regions. When a highly efficient driving is performed, it is demanded that the electrostatic force that suppresses the rotation is reduced.